A flip-chip module is known from U.S. Pat. No. 6,578,754 B1. The contact posts consist of a portion containing substantially copper and a shorter portion consisting of solder material which is connected to the contact points of the substrate. The length of the copper portion is at least 50 micrometers (μm). Contact points are to be contactable with these contact posts, which are disposed in a regular grid, whose grid distance, which is smaller than 100 μm, is preferably in the range of from 80 to 100 μm.
Due to the provision of defined contact posts considerable advantages are obtained as compared with conventional flip-chip modules, which, above all, are that the risk of a short circuit between adjacent contact points is by far less than in conventional flip-chip modules, in which the connection between the substrate and the semiconductor chip is implemented alone with approx. spherical contact elements of solder material. Consequently, it is possible to reliably contact points in a grid of less than 100 μm.
Reference is also made to U.S. Pat. No. 6,550,666 B2 and U.S. Pat. No. 6,592,019 B2, in which further embodiments of the flip-chip module described above are set forth.
Moreover, the flip-chip modules have all advantages of conventional flip-chip modules as compared with wire bonding. The path of the electric conductance between the semiconductor chip and the substrate and thus the signal path is in particular very short.
There is a considerable need to contact several DRAM memory chips by means of a flip-chip module directly without the use of an additional wiring plane, since, on the one hand, due to the plurality of the connections, the conventional contacting by means of wires is practically hardly implementable and, on the other hand, the desired data transfer rates are not possible with conventional wire bondings.
The contact points of these DRAM memory chips are disposed at a grid distance of less than 100 μm, which is referred to as “fine pitch” in the technical jargon. Such a fine pitch can be contacted with the contact posts explained above. Conventional contacting technologies for flip-chip modules are not suitable for this. Moreover, it must be taken into consideration that low k passivation materials are increasingly used for the strip conductors within the chip, which are mechanically weak, for which reason a mechanical tension exerted on such a semiconductor chip results in cracks and fractures in the passivation layer.
The German patent applications DE 10 2005 043910 and DE 10 2005 050150, which have not been published so far, reveal a flip-chip module having a semiconductor chip having contact posts, the contact posts being electrically and mechanically connected with a substrate. A spacer is provided between the substrate and the semiconductor chip which is mechanically coupled at least to the substrate. Due to this, thermal tensions in the flip-chip module are absorbed by the spacer and kept away from the semiconductor chip.
A flip-chip module is revealed by U.S. Pat. No. 6,225,206 B1, which comprises a first substrate which is a chip or a module and a second substrate which is a chip carrier or a circuit card, if the first substrate is a chip. One conductive body each of solder material in the form of a post is formed on the first substrate, the chip, at the contact points. The post may have a height of 50 mils up to about 87 mils. A contact point of the second substrate is electrically connected with this post, a contact bump being provided between the contact point and the post.
U.S. Pat. No. 6,050,476 discloses a flip-chip module, in which a chip is connected with a substrate by means of cold soldering. Here, thin layers of indium are provided on the surfaces of the contact points of the chip and the substrate. If two such contact points are contacted with each other and subjected to pressure, then they are mechanically and electrically connected (cold soldering). Here, the contact points of the chip are preferably substantially larger than the contact points of the substrate, whereby it is possible to position the contact points of the substrate at several different points of the respective contact surface of the chip, which do not overlap each other. This permits the removal of a chip from a substrate and the renewed use of the chip, wherein, in the case of a renewed use, other areas of the contact points are connected in each case with the contact points of the new substrate.
Relatively expensive apparatuses and methods for the reprocessing of flip-chip modules are revealed by U.S. Pat. No. 6,182,884 B1 and DE 199 03 957 A1, with which a soldered connection can be separated and the corresponding solder can be removed.
In all known embodiments of a flip-chip module with a semiconductor chip having contact posts a layer of solidified solder is in each case disposed between the contact points of the substrate and the contact posts.
The semiconductor chips once attached to a substrate cannot be replaced in flip-chip modules. This applies likewise to the flip-chip modules explained above, which have contact posts that are disposed at right angles on the surface of a semiconductor chip and to conventional flip-chip modules such as e.g. ball grid array (BGA) flip chip modules, in which the semiconductor chips are directly connected with the contact points on the substrate by means of a solder globule. Moreover, the soldering methods used here are very expensive since a mask of insulating material must be provided, which ensures that the solder of a specific contact point does not get into contact with a further contact point during soldering and generates a short circuit. It is common to all these flip-chip modules that, upon the separation of the soldered connection, a remainder of the solder remains on the respective contact points of the substrate. The amount of this remainder is not defined, due to which different elevations due to the remainders of the solder are formed at the contact points. A substrate with such uneven contact points can no longer be reliably contacted with a semiconductor chip.
On the other hand, flip-chip modules have already been available for quite some time, which comprise several semiconductor chips on a substrate. If it turns out that a semiconductor chip does not correctly function, then the entire flip-chip module is waste even if the further semiconductor chips on the flip-chip module should be all right, since a single semiconductor chip cannot be replaced.
In order to avoid such problems all semiconductor chips would have to be individually tested in advance. However, the testing of semiconductor chips is very expensive, whereas the testing of a flip-chip module is substantially less expensive than the implementation of several separate tests for the respective semiconductor chips, since the entire flip-chip module can be tested in one testing process and the contact points of a flip-chip module are accessible in a substantially more simple fashion than those of a semiconductor chip.
General economic factors determine whether manufactures risk the high costs of the several individual tests of the semiconductor chips or the high costs of the waste of complete flip-chip modules.